In the last decade, nodular (ductile) iron has become progressively more significant to the commercial casting industry because of its strength and other physical characteristics which can be enhanced by graphite shape control. One recent advance in the art of making ductile iron is treating the molten grey iron metal in the mold for the first time with a magnesium alloy resulting in better graphite nodularity. A granular nodularizing agent is placed in a well or treating chamber in the runner system to meet the hot metal poured into the mold. With this method, normal treatment for nodularization and/or inoculation in the ladle prior to pouring of the mold is eliminated.
Although in-the-mold treatment of grey iron to produce nodular (ductile) iron provides greater economy and improved quality, the state of the art has been unable to cast thin sectioned nodular castings with this method with reliable success. This lack of success is believed to be due to at least two aspects: (a) incomplete filling of the thin mold spaces which prematurely close shut by solidifying metal, and (b) excessive formation of carbides in the more quickly chilled thin spaces resulting in brittle castings and typically improper degree of nodularization.